The joining of large diameter cylinders or pipe is difficult for several reasons. Large diameter pipes are subject to a great deal of flexing and out-of-roundness. Out-of-roundness makes the initial joining difficult and flexing is detrimental to the integrity of the joint. Out-of-roundness is a condition which is practically impossible to eliminate in large diameter cylinders. In this context, "large diameter" refers generally to cylinders having diameters greater than 3 or 4 feet, but it can include small diameters. Flexing in a joint may result from material stress or from the containment of pressures in the cylinders.
The formation of a sealed junction between large diameter cylinders suffers from additional difficulties. In addition to out-of-roundness and flexing, the environment and operating conditions to which the joint may be subjected will adversely affect the sealing capability of the joint. Elastomer O-rings have been used to seal large diameter joints with some success. Typically, an annular groove in one cylinder member will receive the O-ring, allowing it to protrude slightly from the groove. The second cylinder member will adjoin the first member and the junction of the two members will coincide with the placement of the O-ring, thus sealing the function.
Although O-rings have been used in rocket casing joints with some success, they have certain deficiencies which render them inadequate in some circumstances. For example, elastomeric materials are vulnerable to extreme temperature variations. Wide temperature variations can cause such materials to become brittle and much less effective as sealers. The loss of flexibility in the Oring may render the seal ineffective in a flexing, large diameter joint. Further, as the sealed pressure within the casing increases, the ability of the elastomeric Oring to maintain the seal at the joint becomes suspect. As the pressure increases, greater flexing or bulging of the joint may be seen, the the extent that the O-ring seal may be blown out or severely damaged.
A sealed joint between two large diameter cylinders or pipes will preferably be capable of withstanding extreme environmental and operating conditions. The joint and seal must be rugged but yet must be flexible to accommodate flexing or bulging of the cylinder members at the joint without loss of the seal and without damage to the joint or seal member.